Nuclear imaging equipment, e.g., medical equipment such as gamma cameras, must be regularly calibrated to ensure that images produced thereby accurately reflect the subject being imaged. Generally, this calibration is performed using a radiation source of known uniformity as a reference. These sources are also known as sheet sources or flood sources. These nuclear imaging devices generally detect the emission of radiation, such as gamma rays, from a source. In medical applications, the source may be, for example, an implanted brachytherapy seed, a catheter, a biopsy needle, or an ingested or injected radionuclide solution. The devices may include a collimator for channeling emitted radiation to a detector (e.g., a scintillation crystal), which produces a signal based on the direction, location and intensity of the emitted radiation. By collecting and analyzing these signals, an accurate representation of the spatial distribution, location and intensity of the radiation source can be achieved.
Regular calibration of the nuclear imaging equipment helps to ensure that detector signals are accurately converted into a representation of the source. Errors in imaging can result from misalignment, software failure, or electronic failure of parts within the imaging equipment. When the nuclear imaging camera images a known uniform radiation source, such as a flood source, these equipment failures will appear as non-uniformities in the image of the known uniform source. These non-uniformities can be corrected by proper tuning or calibration of the gamma camera or can be accounted for in the capturing of subsequent non-uniform images.
Accordingly, it is important that radiation sources used for calibration have a relatively uniform or, at least, well-known distribution of activity, both in terms of intensity and spatial distribution. Moreover, because such sources must be frequently handled by personnel, it is important that these sources be sufficiently light and durable and that the radiation exposure of handling personnel be minimized.
Current flood sources are generally made of cast epoxy in which a radioisotope is uniformly distributed and sealed within an outer housing of plastic or metal. Such sources are generally bulky and heavy and are difficult and messy to manufacture. Large molds or leveling tables are required to form the epoxy to the desired shape. Moreover, because radiation is involved, a messy manufacturing process that produces significant amounts of radioactive waste residue is unnecessarily expensive.
After a while, radiation sources used for calibration become depleted. When the sources become depleted they are generally returned to the manufacturer for disposal and replacement with a fresh source. Disposal of a partially depleted source creates additional radioactive waste, which is costly to dispose. Moreover, the sources are bulky and are often shipped in shielded containers that are also large and heavy, resulting in high shipment costs in addition to waste disposal costs.
For these reasons, it is desirable to create a radiation source that is lightweight and/or flexible, that minimizes the mass of radioactive waste when replacement is necessary, and that is simple and clean to manufacture.